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Команды помоему нет. Быстрый рецепт для 32-битного слова из Hackers Delight (не уверен что отобразится правильно, но если надо то кину в мыло):
Bit reversal can be done quite efficiently by interchanging adjacent single bits, then interchanging adjacent 2-bit fields, and so on, as shown below [Aus1]. These five assignment statements can be executed in any order.
x = (x & 0x55555555) << 1 | (x & 0xAAAAAAAA) >> 1;
x = (x & 0x33333333) << 2 | (x & 0xCCCCCCCC) >> 2;
x = (x & 0x0F0F0F0F) << 4 | (x & 0xF0F0F0F0) >> 4;
x = (x & 0x00FF00FF) << 8 | (x & 0xFF00FF00) >> 8;
x = (x & 0x0000FFFF) << 16 | (x & 0xFFFF0000) >> 16;
A small improvement results on most machines by using fewer distinct large constants and doing the last two assignments in a more straightforward way, as is shown in Figure 7-1 (30 basic RISC instructions, branch-free).
Figure 7-1 Reversing bits.
unsigned rev(unsigned x) {
x = (x & 0x55555555) << 1 | (x >> 1) & 0x55555555;
x = (x & 0x33333333) << 2 | (x >> 2) & 0x33333333;
x = (x & 0x0F0F0F0F) << 4 | (x >> 4) & 0x0F0F0F0F;
x = (x << 24) | ((x & 0xFF00) << 8) |
((x >> 8) & 0xFF00) | (x >> 24);
return x;
}
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